This invention relates generally to switchgear and more particularly to metal enclosed switchgear of a type suitable for relatively low voltage power distribution service. More specifically this invention relates to front covers having a recessed portion flush with circuit interrupting devices mounted in the switchgear unit and providing a dead front construction.
A metal enclosed switchgear installation usually includes one or more units with each unit consisting of a plurality of sections or cells. The sections are assembled side-by-side to provide a unit or switchgear assembly capable of housing a desired number of circuit breakers or other circuit controlling devices. The maximum number of sections assembled in a unit at the factory is usually governed by the handling and shipping facilities available. The associated main horizontal bus and the vertical risers or conductors are electrically connected at one or more points. For economic reasons it is desirable that the amount of through horizontal bus, vertical section bus, branch bus, load side extensions and interconnecting conductors be kept to a minimum. This can best be achieved by having the horizontal through bus for each phase of a three-phase system spaced apart in a vertical plane behind the vertical section bus. It is also desirable to mount the molded case circuit breakers or other circuit interrupting or controlling devices as close to the vertical section bus as practical so as to reduce the amount of required branch bus and the length of the load side extensions.
Each switchgear section comprises a structural framework in a formed sheet metal enclosure. Each switchgear unit generally has a breaker compartment at the front, a cable compartment at the rear and a bus or conductor compartment between the cable compartment and the breaker compartment. The breaker compartment can be divided into a plurality of individual enclosures for housing circuit breakers or other circuit controlling devices.
The bus compartment contains main through bus bars and vertical riser conductors or vertical section bus to which the branch bus and individual circuit breakers are connected. Loadside conductors extend from the circuit breaker, past the vertical bus, through the bus compartment, and terminate in the cable compartment at the rear of the switchgear cell. In order to keep the length of the loadside conductors and the branch bus to a minimum, it is desirable that the depth of the main bus compartments be kept small and the breakers be mounted close to the vertical bus. When the circuit breakers or circuit controlling devices are mounted close to the vertical section bus the front of the breaker and the operating handles of the breaker are recessed from the front of the switchgear unit. In some prior art switchgear assemblies extensions have been added to the operating mechanism so that the operating handle extension is flushed with the front of the switchgear unit. These operating handle mechanisms add cost to the switchgear unit and complicate the switchgear assembly. As is well known in the prior art, the circuit interrupters normally include a rating indication and magnetic breaker adjustment on the front cover. Also, with the operating handle extensions in place and the front cover plate flush with the switchgear front and not flush with the circuit breaker it is necessary to remove the front cover plate to obtain access to the front of the circuit breaker for adjustment of the external magnetic breaker trip.